This invention relates to a method and apparatus for detecting leaks in liquid-carrying conduits.
The invention is particularly suitable for detecting leaks in mains water distribution systems and will be described principally in relation to that use, However, the invention in its broader aspect may be used for detecting leaks in conduits carrying other liquids.
In many developed countries, water distribution systems contain pipework of considerable age and a high proportion of water may be lost through leakage from pipes. Conventional methods for detecting leaks are slow to use and low in accuracy, and it is common to have to excavate a considerable area in order to discover the precise source of a leak.
An object of this invention is to provide a method and apparatus which will enable leaks to be detected in a relatively simple and accurate manner, and may be used for surveying a network rather than reacting to the events such as subsidence.
From one aspect, the present invention provides a method for detecting leaks in a conduit carrying a liquid, the method comprising deriving, for a series of locations along the conduit, signals related to volumetric flow in the conduit by means of measuring the effects of flow around a relatively large body and around a relatively small body at each said location, and using change in volumetric flow as an indication of the location of a leak.
Preferably, the method comprises passing two test bodies of differing diameters serially through the conduit, detecting pressure differences around each of the test bodies, and using the pressure difference information to derive the volumetric flow rate at said positions along the conduit.
Preferably, the two test bodies are passed through the conduits simultaneously at a predetermined distance apart. Alternatively however, they could be passed through the conduit one at a time.
From another aspect, the present invention provides apparatus for detecting leaks in a conduit carrying a liquid, the apparatus comprising at least one test body to be passed through the conduit so as to provide a relatively large and a relatively small obstruction to flow at locations spaced along the conduit; means for measuring the effects of flow around said obstructions; and means for transmitting said measurements to a remote location at which a measure of the volumetric flow at said locations is derived.
The invention further provides apparatus for detecting leaks in a conduit carrying a liquid, the apparatus comprising first and second test bodies to be passed through the conduit, each of the test bodies being provided with means for measuring the pressure difference around it, and means for transmitting signals representative of said pressure differences to a remote location at which the pressure difference signals are used to derive a measure of the volumetric flow rate of the liquid at locations along the conduit.
Preferably, each of the test bodies is neutrally buoyant in the liquid of interest.
Preferably also, the maximum test body diameter is no greater than 60% of the pipe diameter. Typically, one test body will have a diameter of approximately 50% of the pipe diameter and the second test body approximately 20% of the pipe diameter.
In a preferred form of the apparatus, the two test bodies are connected together by a cord or the like to be passed through the conduit at a predetermined spacing apart, the downstream test body being in the form of an inflatable bladder, and the upstream tests body carrying electronics for transmitting pressure signals to a remote location, suitably via a co-axial cable.
In a particularly preferred form of the invention, the pressure sensors are used also to indicate the presence of localised turbulence, and the presence of a leak is indicated by such localised turbulence in combination with a reduction in volumetric flow downstream thereof.